Ionic discharge devices



June 30, 1959 J. M. N. HANLET IONIC DISCHARGE DEVICES Filed Oct. 28, 1957 FlG.1

MM 48. M WW7 United States Patent IONIC DISCHARGE DEVICES Jacques Marie Noel Hanlet, Paris, France, assignor to Centre dEtudes et de Developpements de lElecu-onique, CEDEL, Paris, France Application October 28, 1957, Serial No. 692,742

Claims priority, application France November 30, 1956 11 Claims. (Cl. 315-55) The present invention relates to improvements in gas or vapour filled discharge devices which operate by the initiation and maintenance of a plasma between a cathode and an anode included within a bulb filled with such an atmosphere. The term plasma as used herein relates to that spatial portion of a gas or vapour atmosphere wherein exists a high and substantially equal concentration of positive and negative charges, viz. of electrons and ions.

An object of the invention is to provide a structure of a discharge tube of a kind which operates as a selfrelaxation device without the application across the cathode and anode thereof of a potential dilference as high as those used 'in conventional structures of this kind of tubes for initiating and maintaining the said plasma therewithin.

According to the invention, such a discharge tube structure is mainly characterized in that it incorporates, in addition to an ionisable gas or vapour atmosphere and at least a cathode and an anode across which is applied a potential diiference of insutficient value for initiating and maintaining the ionization therebetween, at least one condenser element one electrode of which is in direct contact with the said atmosphere and the other electrode of which, isolated from the said atmosphere, is connected to the cathode of the structure, and in which is established a beta ray emitter ensuring a permanent transfer of electrical charges between the electrode connected to the cathode and the electrode contacting the said atmosphere, from which is obtained the required result, which may be explained substantially as follows:

From the permanent transfer of electrical charges across the said condenser electrode and their accumulation on the receiving electrode, the potential difference across the cathode and that electrode of the condenser contacting the said atmosphere reaches the ionization value of the said atmosphere so that the required plasma will be initiated. The electrical resistance of the atmosphere will suddenly drop as, as is well known, such a plasma is a quite good conductor or, in other words, the resistance of the said plasma is quite low; the con denser will abruptly discharge through the plasma and consequently a current of high intensity circulates through the said plasma across the cathode to anode path of the tube and, consequently also, through any load circuit serially inserted in the said circuit; now the discharge of the condenser will bring the potential of the electrode thereof contacting the said atmosphere to a low value and the ionization of the atmosphere will be interrupted; as the transfer of electrical charges is continuous, the thus-described phenomenon process will repeat and consequently the tube will act as a self-sustained relaxation device.

The detailed features of the invention will be described with reference to the accompanying drawings wherein is shown an illustrative embodiment of a discharge tube according to the invention and wherein Fig. 1 and Fig. 2 are respective cross-section views of the structure diagram of the tube and of the structure diagram of the condenser element in the said tube.

The discharge tube comprises a bulb or vessel 1 containing a cathode made of a rod or cylinder 2 coated with an electron emitting layer 3 and an anode 4 coaxial with the cathode and practically surrounding the said cathode member. It may be considered that the cathode will be, in most of the applications of the invention, of the cold cathode type, and the recourse to a thermionic cathode will only be the fact of very high powers required from the device. The anode 4 is interrupted along a sector of small span as indicated and, within the said sectorial space is mounted a condenser structure which may, as detailed more definitely on the cross-section of Fig. 2 thereof, include an outer cylindrical electrode 7, an inner coaxial electrode 5 and, over the inner face of the cylindrical electrode 5 is made a coating of a radio-isotope 6 of thekind which emits a beta ray emission. Obviously for the sake of clarity, the respective thicknesses of the elements are not preserved in the drawing.

An electrical conductor 8 connects the cathode to the inner electrode 5 of the said condenser member. It is immaterial for the invention that such a connection be made within the bulb of the tube or externally therewith. The seals and spacers are omitted on the drawing, for the sake of simplicity, all being of a quite conventional technique, as is well known.

The condenser being of a coaxial structure in the embodiment shown as an illustrative example thereof, insulated plates 12 and 13 together with the conducting rod 8 are used for supporting the structure. Conducting members 14 and 15 connect the rod 8 to the inner electrode 5 and support this electrode therefrom. The plates 12 and 13 support the outer armature 7 for instance through vacuum-tight joints and the conductor 8 is also vacuum-tightly sealed through these plates, which are for instance made of ceramics or glass. The internal volume of the condenser is evacuated by any suitable process. The use of an exacuated vacuum-tight condenser is not imperative per se, as solid-state dielectric condenser may be used, but it is thought preferable as favouring a very high leak resistance of the unit which is required for not having a too high capacity value of the condenser and consequently a too high volume thereof. It is apparent that the capacity of the condenser is one of the factors which govern the recurrence frequency of the self-relaxation of the device.

The inner electrode 5 is constituted by a thin nickel cylinder of say 25 microns in thickness. Over the inner face thereof is made a deposit of a radio-isotope emitting beta rays. The use of beta rays is provided in order to facilitate the handling of such a radio-isotope. It may be coated as a pure element, from a thermic evaporation process for instance, or as a salt, from a chemical reaction of the said isotope with the material of the wall of 5 for instance or else from a precipitation or sedimentation process, according to a technological choice unaifecting the invention proper. One may provide radio-isotopes having a very wide span of useful lives, from some months to several tens of years, or even thousands of years so that the designer will not have any difiiculty in this respect. For instance, one may cite thallium 204 the useful life of which equals 2.7 years, silicium 31 the useful life of which equals 14 years, and so forth.

Whatever is the radio-isotope, the deposit only needs a film of this substance, at 6, and the particles therefrom pass through the thin wall 5 which only has a quite small absorption coefiicient for the said particles. When nickel is used with the above-defined thickness, the said absorp ice tion factor is lower than The beta particles pass through the dielectric of the condenser and reach the electrode 7 with a high velocity. The electrical charges thereof deposit on the said outer electrode 7 and the storing of these electrical charges thereon increases permanently the potential of the said electrode 7 up to the point where at is reached the ionization potential difference of the atmosphere of the tube across the cathode and the said electrode.

Across the cathode and anode of the tube is applied a potential difference determined by the voltage of a battery 9. This potential difference, as stated, is not required to be high. For a filling of quicksilver vapour for instance, or of cadmium vapour, it may remain lower than 6 volts; for a filling of hydrogen, nitrogen, argon, krypton or xenon, for instance, it may remain lower than 12 volts; and for a filling of helium or neon, for instance, it may remain lower than 24 volts. The anode potential does not interfere with the initiation and maintenance of the plasma within the tube but only in the determination of the current passing through the said plasma controlled from the said potential difierence. This plasma will be of extremely low resistivity any time it will exist due to the relaxation operation of the tube. From a certain point of view, consequently, a device according to the invention may be considered as acting as a converter of a low D.C. voltage into a high AC. voltage through a purely electronic process. The meaning of A.C. is here quite broad since it relates to a relaxation oscillation so that, at first sight at least, the voltage collected across a resistive load serially connected in the anode to cathode circuit of the tube has a saw-toothed waveform. However, as known, the deionization time interval of a gas or vapour filled tube is far from negligible, which has as a first action to render the saw-tooths less asymmetrical in the waveform thereof. Such a phenomenon is usually considered as a drawback of conventional tubes for switching purposes but, to the ends reached at by the invention, it is an advantage which may be enhanced by introducing a certain amount of metastable gas within the bulb of the tube. The collected waveform then approaches a triangular wave-shape, quite easy to convert into a substantially pure sine wave through the introduction of simple filtering means in the load circuits, when required. The use of a transformer 10 which is shown on the drawing ensures such a result as the triangular wave-shape is integrated by the self-inductance of the primary of the said transformer.

The relaxation frequency is, quite apparently, determined by the following factors: capacity value of the condenser, transfer current (or leak resistance) across the electrodes thereof, ionization potential value of the atmosphere within the tube. The transfer current depends for a given weight of radio-isotope, on the load resistance constituted by the leak resistance across the condenser electrodes, otherwise termed, on the parallel resistance of the condenser. Further it depends on the activity characteristics proper of the isotope. Consequently, in designing the device, one may either compute the recurrency of the discharge per microgram of a determined isotope or, conversely, the weight of a determined isotope necessary for obtaining a required recurrence frequency, all other conditions being identical per se. Illustratively, and for specially pointing the smallness of the weight of radio-isotope which will usually be required in a device according to the invention, a recurrence of one second is obtained with a microgram of silicium 31 with a capacity value equal to 10 picofarads and for a ionization potential equal to 100 volts of the inner atmosphere of the tube.

However, during the course of utilisation of such a tube, the recurrence frequency will be subject to support variations, if the ambient temperature varies. When this is the case, the product volume pressure within the tube will, as is well known, vary according to a linear relation with the external temperature. of course, temperature deviations could only occur within a restricted range, for instance between 40 and +1l0 C. Negative temperature coefiicient condensers are known, and linearly responsive to such changes of temperature. Consequently, such condensers may be used in a device according to the invention for maintaining at a constant value the recurrence frequency of operation within this range of temperatures. For instance, such a negative temperature condenser will be connected in shunt with respect to the condenser making part of the structure of the discharge tube, leads being provided for such a connection from the electrodes 5 and 7 of the inner condenser of the tube through the bulb thereof. Of course, when such a correction is due to be provided in the very design of the tube, the temperature coefiicient correcting condenser may be provided with such a shunt connection within the very bulb of the tube.

From another point of view, it may be of advantage to be able to provide for, when required, an adjustment of the recurrence frequency of operation of the relaxation device. This may also be made by the shunt connection of an auxiliary condenser across the electrodes of the inner condenser of the tube, viz. across leads from the electrodes 5 and 7 of the said inner condenser passed through sealed joints in the bulb of the tube. It is only an adjustment which is to be contemplated here, and not truly a change of recurrence frequency as, if the controlling capacity was the externally connected one, the efficiency of the device would be apparently reduced since the transfer and storing of electrical charges cannot be varied as imposed by the internal structure of the tube.

Of course, the internal geometry of the disclosed tube may be modified at will without departing from the scope of the invention, and a control grid may be added if required.

I claim: 1

1. A self-relaxation device comprising a gas plasma discharge tube comprising a sealed envelope containing a gas atmosphere, at least an anode and a cathode, means for establishing a potential difference across said anode and cathode which is low with respect to the ionization potential of the said atmosphere through a circuit including at least one serious load therefor, and at least one condenser element within the envelope, one electrode of said condenser being in contact with said atmosphere, means mounting the other electrode of said condenser out of contact with said atmosphere, means electrically connecting the other electrode to the cathode, a radioactive emitter material carried by the other electrode for transferring to and storing electrical charges on the one electrode to produce a potential difference between the cathode and the one electrode of a magnitude sufficient to cause ionization of the gas.

2. A combination according to claim 1 in which the electrodes of the condenser element are substantially cylindrical and in coaxial relation.

3. A combination according to claim 1 in which the anode and the cathode are substantially cylindrical and in coaxial relation, the continuity of the anode wall being interrupted to form a space, said condenser element being mounted in said space.

4. A combination according to claim 1 in which the electrodes of the condenser element are substantially hollow cylinders one of which coaxially surrounds the other, the beta particle emitter being mounted within the inner electrode.

5. A combination according to claim 1, wherein the dielectric of the said condenser element is a vacuum.

6. A combination according to claim 1 and wherein the dielectric of the said condenser element is a solid dielectric.

7. A combination according to claim 1 and wherein the gas filling of the envelope further contains a small ount of metastable gases.

8. A combination according to claim 1 and wherein the said beta particle emitter consists of a radio-isotope.

9. A combination according to claim 1, wherein a negative temperature coeflicient condenser is connected across the electrodes of the said condenser element.

10. A combination according to claim 1 and wherein a frequency adjustment impedance is branched across the electrodes of the said condenser element.

11. A combination according to claim 8, wherein the said radio-isotope is selected from a group comprising silicium 31, thallium 204 and salts of these materials.

References Cited in the file of this patent UNITED STATES PATENTS Ainsworth July 6, 1915 Loewe Feb. 25, 1930 Linder May 8, 1951 Coleman Oct. 2, 1951 Coleman Nov. 4, 1952 Linder Feb. 16, 1954 Alvarez Mar. 16, 1954 Franks et al July 10, 1956 Cohen Apr. 16, 1957 

